There is a fortnight or so each summer when the hedgerows turn frothy with elderflowers, and if you blink you will miss it. The window usually opens in late May in the south and early June further north, and it closes almost as soon as the flowers begin to brown and drop. Make a batch of cordial now and you will have the taste of an English summer in the fridge for months, ready to be diluted with sparkling water on a hot afternoon or splashed into a gin and tonic on a warm evening.

Elderflower Season: What to Look For

Elderflowers grow on the elder tree, a scrubby hedgerow regular that is often overlooked until it flowers. You want the heads at their peak — creamy white, fully open, with a scent that is somewhere between lychee, muscat grape and a squeezed lemon. Pick them on a dry, sunny morning once any dew has dried, because damp flowers dilute the flavour and can turn mouldy in the bucket.

• Choose fully open, creamy heads with a strong fragrance. Leave any that are turning brown or dropping petals.
• Avoid busy roadside verges and sprayed hedges. Field edges, quiet lanes and garden trees are better.
• Pick more than you think you need — you will discard the thickest stalks — and leave plenty behind so the tree can set berries for the birds.
• Don't wash the heads. You would rinse away the pollen, which carries much of the flavour. Simply shake them gently over the bag to dislodge any insects.
• Use them the same day if you can. If not, spread them in a cool place and use within twenty-four hours.

The Classic Cordial Recipe

This is the traditional method, and it makes roughly two litres of finished cordial — enough to see you through the summer. Citric acid is the key to both the flavour and the shelf life; it sharpens the sweetness and helps prevent spoilage. You will find it in chemists, homebrew shops and the baking aisle.

• 1.5 litres water
• 1kg granulated sugar
• 30g citric acid
• 2 unwaxed lemons
• 20–25 large elderflower heads, stalks trimmed

Put the water and sugar into a large pan and bring slowly to a simmer, stirring until every grain of sugar has dissolved. Do not let it boil hard. Take the pan off the heat, stir in the citric acid and leave to cool until just warm.

Pare the zest from the lemons in wide strips, avoiding the bitter white pith, then slice the lemons thinly. Add both to the pan along with the elderflower heads, pushing them down into the liquid. Cover with a clean cloth and leave at room temperature for twenty-four to forty-eight hours. Stir once or twice a day. The longer it sits, the more floral it becomes — but beyond two days it starts to taste grassy.

Straining, Bottling and Storing

Line a large sieve with a double layer of muslin and set it over a big jug or bowl. Ladle the mixture through and let it drip. Resist the urge to squeeze the pulp hard — a gentle press is fine, but a firm squeeze pushes out bitter, cloudy sediment.

Funnel the cordial into sterilised bottles. To sterilise, wash bottles and caps in hot soapy water, rinse well, then place them in a low oven at about 140°C for fifteen minutes until completely dry. Fill while the bottles are still warm, seal and label with the date.

Kept in the fridge, cordial made with citric acid will last two to three months. Once opened, use within a few weeks. If you would rather not use citric acid, the cordial will still work beautifully but should be kept chilled and used within a fortnight. For longer storage, freeze it in ice cube trays and drop a cube or two straight into a glass.

Alcohol-Free Ways to Serve It

The classic dilution is one part cordial to five parts water, but taste as you go — some batches are punchier than others. For a long, refreshing summer drink, pour 30ml over ice, top with chilled sparkling water and add a slice of lemon, a sprig of mint or a few raspberries.

• Elderflower lemonade: mix cordial with still water, a squeeze of fresh lemon and plenty of ice.
• Iced tea: stir a spoonful into cold jasmine or green tea with sliced cucumber.
• Fruit salad: drizzle undiluted cordial over strawberries, peaches and mint.
• Sorbet: dilute a little less generously, freeze in a shallow tray and fork through every half hour.
• Sparkling elderflower pressé: add a splash of cordial to equal parts apple juice and soda water.

For Grown-Ups: Gin, Prosecco and Cocktails

Elderflower and gin are natural companions — the floral notes pick up the botanicals without overwhelming them. A measure of gin, a good glug of tonic, 15ml of cordial and a strip of lemon zest over ice makes an excellent warm-weather drink. Swap the tonic for soda and add a sprig of thyme for something drier.

For a celebratory pour, add 15ml of cordial to a flute before topping with chilled prosecco or English sparkling wine. It also works a treat in a spritz: 30ml cordial, 30ml dry vermouth, plenty of ice and soda water, finished with a slice of cucumber.

Troubleshooting and Little Variations

If your cordial tastes flat rather than floral, you probably steeped it too briefly or picked flowers past their best. If it is cloying, add a little more lemon juice or citric acid at bottling. A slight haze is normal and harmless.

Should you spot bubbles or a fizzy smell after a week, the cordial has begun to ferment — discard it. To ring the changes, steep a few strips of orange zest with the lemon, add a handful of mint leaves for the last few hours, or use half the sugar and keep the cordial strictly refrigerated for a lighter, more delicate result. Whatever you choose, make two batches while the elderflowers are out. The second one always disappears faster than you expect.